Americans seem to have an almost pathological blindness to seeking out the experience of other countries.
That's not even true in the developed world, much less so in the rest (where ethnic or religious conflicts often lead to disastrous consequences). It's just that Americans sometimes have a narrow lens when it comes to diversity: "they're all white (or all black), so they must all think the same, speak the same language, have the same religion, etc." Linguistic diversity, for example, is much greater even in individual European countries than in the US.
I'm certainly not making the absurd claim you're proposing that "they're all white so they're the same thing". What I am claiming is that, partially due to the relative population sizes, the "white" population of somewhere like France is more homogeneous in cultural tradition. Obviously there's some amount of cross-migration between EU countries, but most of the US's "white" population is, obviously, non-native within the last 3-6 generations, and from all over Europe mostly. Obviously not all of China or India is exactly the same culturally, but those are both countries who have a core cultural history for their residents that goes back far before the US was even a thing, and that tends to provided a basis for the more specific cultures that are different, providing some commonalities.
Same with religion - while the US is predominantly Christian, it's essentially the breeding ground for almost every major denomination of Protestant church/new faith movement, compared to countries that have a strong Catholic-specific background. Just structurally, the teachings and culture of US Protestant/Evangelical churches are more different from each other than what I've seen within more top-down Catholic or Muslim communities I've interacted with.
You're certainly right about countries with a history of ethnic conflict, "developed" or otherwise, but many of those are majority religions/cultures fighting minority ones in an attempt to create a homogeneous state, and separately, I'm assuming OP didn't imply that the US should be looking to Yemen or Ethopia for examples on how to solve problems of cultural issues at this point.
I'm not even sure about the linguistic part. Per US Census in 2017, only 78% of US households speak English at home, compared to 90% of residents in Germany speaking German at home according to a 2019 Pew Survey, or 92% of people in England and Wales speaking English per a 2011 Census there.
Countries like Switzerland, Belgium etc. are linguistically divided with no one language common to all. Even countries with one dominant language (e.g. Germany) have regional minority languages (e.g. Danish). Russian-speaking people live in Ukraine (without being "Russian" in any political sense) or in Belarus. Swedes live in Finland. Yugoslavia fell apart because of ethnic tensions between groups of people that are linguistically close, but religiously diverse (Catholic, Orthodox and Muslim), and there are still Serb minorities in Croatia and vice versa. In general, the history of Europe is littered with people that are not that culturally different going at war with each other, or treating each other like shit, without the need for there being a difference in skin colour (just consider the 30 years war, for example). It's calmed down in the last century, but it still reverberates throughout society.
edit: Forgot to mention Spain with its decades-long tension between the central government and Basque or Catalan separatists.
edit2: You mentioned India. India has 23 official languages.
But the data doesn't seem to point to this, at least any more than other countries. More households, almost definitely by absolute numbers but also in percentage, in the US are predominantly speaking a language other than the official language of the country than almost anywhere in Europe.
The fact that Europe has a history of strife among culturally similar people seems to, if anything, prove my point? A lot of Europe is culturally similar, and yes, often the dividing lines are arbitrary and strange, but that diversity is a little different than the US. It's not as if Oregon is just all of the people in one cultural minority in the US, whereas sub-groups in Europe are often geographically distinct to some degree. Scotland, Calalan, plenty of bits of Eastern Europe, while a part of a larger country legally, are distinct cultural units. In the US, there's almost never that stark of a division larger than a specific neighborhood in a larger city.
Yes, Swedes live in Finland and countries like Austria have multiple official languages, but my original point is that, culturally, most people in Finland and Austria have more cultural similarity to their neighbors than I do with the 2nd generation Chinese immigrants that live on one side of me and the French-Creole couple on the other side.
I feel like we've gotten a bit afield from the original dispute though. The OP was implying that the US was being ignorant for not seeking counsel from other countries about cultural topics like gender differences. My issue with that is that it implies that there's an obvious solution to the US's cultural problems in some other country, when it's likely that the reason men or women may be struggling in the European/Protestant immigrant community may be different from why they're having issues in the Indian/Hindu immigrant community, which is likely different from the Indian/Muslim community and the Central American/Catholic community or the 5th generation Gen Z Caucasian Atheist community.
Handling and diagnosing each of those are likely different, and at a whole-country level, the US probably can't just try to import a solution that worked in the UK and think it will work broadly here. On the other end, I'd imagine groups in the US probably are looking at what groups in the home country of various immigrant populations are doing and sharing ideas, but that's likely happening at a level you won't know about unless you're in those communities.
In general, the US, even regionally or locally, isn't as close to being a monoculture in the same way many of the towns and regions in Europe or Asia are. I don't mean this to say that either way is better or worse, but that when it comes to values and culture, there's often much less of a shared understanding and history, which can make sharing large-scale social initiatives harder.
Do you think there are no Chinese immigrants in European countries?
My examples were about people who have been living natively in certain areas for centuries. Of course, on top of that, we have had immigrants from all over the world in recent decades: Turkish people came to Germany in large numbers in the 50s, Tamil people fleed Sri Lanka in the 90s and came also to Europe, then all the refugees from the Balkan Wars and more recently from Syria and Ukraine, ...
Is NYC more ethnically and culturally diverse than a random mountain village in Austria? Yes, for sure. But Berlin is also more diverse than some random town in Montana. That's just a feature of big cities.
As a whole, though, I feel you're severely underestimating the cultural diversity in Europe.
We have the exact same problems with different cultural segments of the population having distinct discourses about important issues such as gender roles, LGBTQ, COVID, the war in Ukraine, etc.
I would argue the current anti-car movement in the U.S is a result of more americans going abroad for vacation to Europe and Asia and seeing what works there and bringing those ideas back. But how easy is it for Americans to go abroad? Most can't.